A cache memory typically stores data that is more frequently used for fast access in order to avoid the delay of retrieving data from a main memory. The data is stored in the cache memory in one or more storage locations known as lines. Each line includes the data and tag information identifying what data is stored in the line. The tag information includes an address field and various control fields and bits. The number of fields and bits for control is relatively small and may limit the amount of control information that may be carried therein. Real time performance of a cache can be improved by setting a lock bit associated with a cache line so that the cache line data cannot be evicted from the cache for being least recently used. Since every data entry needs a lock bit, the cost of a lock bit can be significant with large cache sizes.